1. Field of the Invention
The present invention relates to vehicle sensors and, more specifically, to a vehicle sensor that determines the location and size of an occupant of a vehicle.
2. Description of the Prior Art
The performance of an air bag system, in terms of its success or failure in preventing serious passenger injury, may depend on the size and position of the passenger. For example, if the passenger is seated too far forward or is relatively small, the passenger may be seriously injured by the deployment of the air bag.
Several different types of devices may be used to determine the passenger""s position and size. One of these is the capacitive coupling sensor. In such a sensor, a capacitor is formed by a plurality of charged plates surrounding the passenger area of the vehicle. A change in capacitance is caused by the nearby presence of an occupant of a vehicle. An overhead array of capacitive coupling proximity sensors, the signals from which are analyzed by a microprocessor, allows essentially instantaneous and continuous monitoring of passenger position and motion through triangulation based on the distances of the passenger to the various sensors of the array.
One type of capacitive sensor employs a conductor on a seat and other conductors that are disposed about the vehicle body as electrodes. The electrodes and the inter-electrode compartment space in which the person is seated forms a capacitor. Sensing of the inter-electrode capacitance allows determination of the presence and absence of a person in the compartment. When the person takes a seat, the capacitance of the capacitor is increased and the increase in capacitance may be sensed with one of several types of circuit to determine the presence of the passenger. Such capacitive circuits have a disadvantage in that they are susceptible to noise and have a limited range.
Therefore, there is a need for a passenger sensor with a wide range that resists the effects of noise.